To determine how extended high frequency is affected by noise exposure and other factors that maybe have adverse effects.

Pure tone audiometry for usual frequencies (250–8000 Hz) and extended high frequencies (1000–16000 Hz) was conducted for 331 workers at a manufacturing company from 2004 to 2005. History of noise exposure, military service, tinnitus, alcohol drinking, smoking, ear diseases, and noisy hobbies were taken by interview. T-test, ANOVA, and multiple regression was conducted according to the frequency to evaluate the factors that could affect extended high frequency hearing.

The noise-exposed group had significantly poorer hearing than the noise-unexposed in the frequency range 2000–16000 Hz. The hearing deteriorated with increasing age through all the frequencies. High frequency hearing of 14000 Hz was significantly worse in the noise-exposed group in their 30s. Noise exposure during military service had a bad effect on hearing, especially for the noise-unexposed group. Tinnitus was associated with poorer hearing in both noise-exposed and noise-unexposed groups. Workers with noisy hobbies exhibited better hearing in the noise-unexposed group, contrary to our expectation. Extended high-frequency hearing was affected by aging, ear protection, and noisy hobbies. In extended high frequency, 14000 Hz was especially related with noise exposure history.

Extended high frequency, especially 14000 Hz, could be used as an indicator of noiseinduced hearing loss and should be considered as a screening test for workers in noisy environments.